Microwave endoscope detection and treatment system

ABSTRACT

The microwave system is employed for the detection of cancerous tumors and is particularly effective in the early detection of such tumors. The system is of the dual type, combining in a single unit a passive radiometer with an active microwave transmitter. The sensitive passive microwave radiometer is adapted to sense subsurface temperatures, coupled with a solid state microwave transmitter for providing localized heating of the subsurface tissue, thereby taking advantage of the differential heating due to vascular insufficiency associated with the thermal characteristics of tumors, thus highlighting and enhancing early detection of cancer. A delay period on the order of five minutes is defined between heat application and detection in order to optimize temperature differential. The transmitter or applicator is for internal use employing a radiating element adapted for use with an endoscopic apparatus.

RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 135,506 filedMar. 31, 1980 now U.S. Pat. No. 4,346,716.

BACKGROUND OF THE INVENTION

The present invention relates in general to an improved passivemicrowave detection technique for early detection of cancerous tumors.More particularly, the invention relates to a system adapted to providelocalized heating of subsurface tissue with the use of an activemicrowave transmitter in combination with a passive radiometer fordetecting a temperature differential occasioned by the differentialheating between the tumor and adjacent tissue.

Studies have been conducted on the ability to measure temperaturegradients particularly deep within the body tissue in connection withclinical medicine and research. For example, see the articles to A. H.Barrett, P. C. Myers and N. L. Sadowsky, "Detection of Breast Cancer byMicrowave Radiometry." Radio Science 12, No. 6(S), 167, 1977; Ronald A.Porter and Harry H. Miller, "Microwave Radiometric Detection andLocation of Breast Cancer." (Preprint.); J. Bigu del Blanco and C.Romero-Sierra, "MW Radiometry: A New Technique to Investigate theInteraction of MW Radiation with Living Systems." 27th ACEMB,Philadelphia, Pa., 6-10 Oct. 1974. These temperature gradients occur, itis theorized, because of vascular insufficiency associated with thethermal characteristics of tumors. It is well known that a carcinoma ormalignant tumor is normally hotter than the surrounding tissue. It isalso known that, from "black body" theory, any perfectly absorbing bodyemits radiation at all frequencies in accordance with Planck's radiationlaw. A recent article on the differential heating characteristics is oneby B. C. Giovanella, "Correlation of Thermosensitivity of Cells to TheirMalignant Potential." Conference on Thermal Characteristics of Tumors:Applications in Detection and Treatment; New York Academy of Sciences,Mar. 15, 1979.

The application of thermal therapy (i.e., localized heating) has beenused to reduce tumor size or to even destroy the tumor. It has beenfound that tumor temperatures greater than 45° C. can be maintained withthe normal tissue adjacent to the tumor at the same time remaining at ornear normal body temperature. It has been reported by severalinvestigators that cell tumor tissue will necrose at temperatures above42° C. See the articles by David N. Leff, "Hyperthermia-Hottest News inCancer Therapy." Medical World News, May 14, 1979; Jozef Mendecki,Esther Friedenthal and Charles Botstein, "Effects of Microwave-inducedLocal Hyperthermia on Mammary Adenocarcinoma in C3H Mice." CancerResearch 36, 2113-2114, June 1976; James Schaeffer, "Treatment ofMetastatic Osteogenic Sarcoma in Mice with Whole Body Hyperthermiaand/or Irradiation." International Symposium on Cancer Therapy byHyperthermia and Radiation, Washington, D.C., 1975. Thermal therapy usedin conjunction with other conventional techniques involving drugs orradiation has proven to be effective (i.e., anti-cancer drugs act moreeffectively at elevated temperatures and, similarly, permit lower levelX-ray treatment). The combination of microwave detection with infra reddetection is reported by Barrett and Myer, supra.

In accordance with the present invention, there is provided a sensitivemicrowave radiometer technique for sensing subsurface temperatureswherein the technique is not invasive. It has been common in the past toemploy a conventional thermistor probe inserted in the area of thetumor, and studies have been made with regard to the effect on theheating patterns induced by microwave diathermy apparatus. See theArticles by Thomas C. Cetas, "Temperature Measurements in MicrowaveDiathermy Fields: Principles and Probes." International Symposium onCancer Therapy by Hyperthermia and Radiation, Washington, D.C., 1975;Len Yencharis, "Temperature Probe Designed For Cancer Therapy."Electronic Engineering Times, 18, Jan. 9, 1978. The results of thesestudies indicate that the heating pattern is altered considerably by thepresence of the sensor.

The microwave radiometer of the present invention is in effect a verysensitive radio receiver capable of measuring temperature differentialsdown to 0.1° C. or less. The receiver, when provided with a highlydirectional antenna and technique of observation, provides a reading ofpower picked up by the antenna. As mentioned previously, any perfectlyabsorbing body emits radiation at all frequencies in accordance withPlanck's radiation law. The distribution of radiation is a function ofboth the temperature and wavelength or frequency. As the temperature ofthe body increases, the density of the radiation at all frequencies alsoincreases. From this viewpoint, infra red thermography or radiometry,appears to be effective, however, the depth of penetration (depth ofeffective emission) becomes a limiting factor. The highest value ofradiation density occurs in the optical region. Nevertheless, anappreciable amount of radiation exists at the microwave segment of thespectrum. In accordance with the present invention the power accepted ina known bandwidth by an antenna having defined characteristics can beaccurately computed as a function of the temperature of the emitter.

As mentioned previously, a carcinoma or malignant tumor normallyradiates more heat than the surrounding tissue. See the article by R. N.Lawson and M. S. Chughtai, "Breast Cancer and Body Temperature."Canadian Medical Association, Vol. 88, Jan. 12, 1963. Early detection,namely detection prior to invasion or metastases, requires the detectionof tumors less than five millimeters in diameter with an associatedtemperature deviation of less than 0.2° C. It has been found inaccordance with the techniques of this invention that such earlydetection is quite accurate, and that tumors of relatively small sizecan be detected which heretofore have not been capable of detection bysuch conventional techniques as X-ray mammography.

Accordingly, one of the objects of the present invention is to providean improved technique for the diagnosis and treatment of canceremploying a non-invasive microwave detection system.

Another object of the present invention is to provide in a single unitthe combination of both a microwave transmitter or source and a passivedetector or microwave radiometer.

A further object of the present invention is to provide a microwavesystem employing a sensitive passive microwave radiometer particularlyadapted for sensing subsurface temperatures in combination with a solidstate microwave transmitter for providing localized heating ofsubsurface tissue. With such a combined system, there is essentially ahighlighting of the tumor to enhance detection, thus taking advantage ofthe differential heating characteristics of the tumor with respect tothe surrounding tissue.

Still another object of the present invention is to provide an improvedmicrowave system for the early detection of cancer and which is adaptedfor use, not only for detection purposes but also for treatmentpurposes.

Still a further object of the present invention is to provide amicrowave system for cancer diagnosis which is totally battery operatedto thus eliminate possible problems associated with line transients andthe like.

Another object of the present invention is to provide an improvedmicrowave system for the detection of cancerous tumors and which isnon-invasive, thus, not requiring the use of any temperature sensingprobes. The present invention employs a sensitive passive microwaveradiometer particularly designed to sense subsurface temperatures.

Still another object of the present invention is to provide an improvedmicrowave system for the detection of cancerous tumors and which iscapable of sensing at a temperature resolution down to at least 0.1° C.

A further object of the present invention is to provide an improvedmicrowave system for the detection of cancerous tumors and which isparticularly adapted for the detection of relatively newly-formed tumorsof extremely small size.

Another object of the present invention is to provide, in a microwavesystem, an improved, extremely sensitive passive radiometer capable ofmeasurements of temperature deviations even less than 0.1° C.

SUMMARY OF THE INVENTION

To accomplish the foregoing and other objects of this invention, thereis provided in accordance with the present invention, a microwave systemfor the diagnosis of cancerous tumors employing non-invasive microwavetechniques. This system may also be employed in the treatment of cancer.The system is preferably totally battery operated, thus eliminating anypossible problems associated with line transients, pickup, etc. Thesystem comprises a sensitive passive microwave radiometer particularlyadapted for sensing subsurface temperatures, in combination with a solidstate transmitter that provides localized heating of the subsurfacetissue. This localized heating essentially enhances the tumor from atemperature differential standpoint, taking advantage of thedifferential heating due to vascular insufficiency associated with thethermal characteristics of tumors. This technique highlights andenhances the early detection of cancer tumors. The selection of both theradiometer and the transmitter frequencies is based upon the followingfactors:

1. Emissivity, which increases with increasing frequency;

2. Spatial resolution; and

3. Microwave transmission characteristics.

In the embodiment disclosed herein, the frequency for the radiometer isselected at 4.7 GHz sufficiently removed from the selected microwaveheating frequency of 1.6 GHz.

An applicator forms the means by which the system couples to the body.This applicator employs a simple TE₁₋₀ mode aperture that is placed indirect contact with the radiating or emitting surface. The aperture isformed by a single-ridged waveguide which is preferred because its uselowers the frequency at which cutoff occurs. To further reduce the sizeof the aperture, dielectric loading is employed. The waveguidedimensions for operation at L-band and the dimensions of the ridgedportion of the L-band ridged wave guide are selected to allowpropagation of the higher frequency associated with the C-bandradiometer. By having the radiometer input contained within thesingle-ridged waveguide. L-band transition, the point of maximum fieldof the source of the heat is in close proximity with the area of thermaldetection. The cut-off characteristics of the C-band waveguide areutilized in addition to other filtering that is provided; the waveguideforming a high pass filter to isolate the high power L-band source fromthe sensitive radiometer. A heater and proportional thermostat areprovided in the dual mode transition or antenna (applicator) to maintaina constant temperature at or very near to the temperature of the humanbody.

Another advantage of the system of this invention is that when theapplicator is uncoupled from the human body, the level of radiation isvery small and well within safety standards. This advantage is realizedby the large mismatch associated with the low impedance ridged waveguidewhen left open-circuited. When so removed, there is a mismatch with theatmosphere which has a low dielectric constant. The measured radiationlevel one inch from the waveguide opening with the L-band source fullyoperating is well within safety standards. For example, one powermeasurement was less than 0.4 mW/sq. cm. The safety standard establishedby the federal government is 10 mW/sq. cm.

The system of this invention is adapted for use both as an applicatorapplied externally to the body and furthermore may be usedendoscopically. The endoscopic version may be used for the effectivetreatment and detection of some cancers.

BRIEF DESCRIPTION OF THE DRAWINGS

Numerous other objects, features and advantages of the invention shouldnow become apparent upon a reading of the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of the microwave radiometer employed inthe system of this invention;

FIG. 2 is a schematic diagram of the L-band transmitter employed in thesystem;

FIG. 3 shows the body transition element in the form of a hand-heldapplicator;

FIG. 4 is a perspective view of the dual mode antenna and waveguideconstruction;

FIG. 5 is a side view of the waveguide construction depicted in FIG. 4;

FIG. 6 is a graph of frequency response for the bandpass filter of FIG.1;

FIG. 7 is a graph of transmitter output level associated with thetransmitter of FIG. 2; and

FIG. 8 is a cross-sectional view of a bronchoscope apparatus adapted toaccommodate a different form of applicator in accordance with anendoscopic version of the invention;

FIG. 9 is a first embodiment of the radiating element of the endoscopicversion; and

FIG. 10 is an alternate form of the radiating element of loop-type.

DETAILED DESCRIPTION

The microwave system of this invention comprises an extremely sensitivepassive radiometer capable of measurements of temperature deviations ofless than 0.1° C. The dual mode microwave system also employs a solidstate transmitter to provide localized heating of the cancer site. Inthe particular arrangement described herein, the C-band radiometerfrequency is 4.7 GHz and the L-band transmitter frequency is 1.6 GHz.The system also includes a dual mode antenna comprising a C-bandaperture in combination with an L-band applicator. The microwavetransmitter causes an elevation of the temperature of the tumor abovethat of the surrounding normal tissue to thus enhance the detection byhighlighting the tumor with respect to the surrounding or backgroundtissue. The heating of the cancer site results in a differential heatingof the tumor with respect to the surrounding tissue. Also, becausetemperatures above about 42° C. are lethal to tumor cells, the system isalso applicable for the treatment of cancer.

As mentioned previously, the system is preferably totally batteryoperated, allowing approximately 8 hours of continuous service prior torequiring a recharging. Such a battery operated system is employed as iteliminates possible problems associated with line transients, pickup,etc. A battery charging circuit is included in the system with anovernight charging cycle being designed to provide the batteries in afully charged condition for the next day's use. Three sealed,maintenance free, lead acid batteries are connected in series, providinga maximum voltage of 36 volts.

FIG. 1 is a schematic diagram of the microwave radiometer of thisinvention. FIG. 2 shows a schematic diagram of the transmitter employedin this system. The radiometer and transmitter both couple to the dualmode antenna with the radiometer receiving its signal from the C-bandaperture and the transmitter directing its signal to the L-bandapplicator. Accordingly, a discussion of the dual mode antenna receivesa discussion hereinafter of the radiometer and transmitter schematicdiagrams.

As previously mentioned, the frequency selected for localized heating is1.6 GHz. For this frequency, a normal waveguide transition that wold beused would have dimensions of 5.100" (12.95 cm)×2.550" (6.48 cm). Thesedimensions correspond to a WR-510 guide. Thus, to reduce the physicalsize of the applicator aperture a single ridged waveguide constructionis used. The use of a ridged waveguide lowers the cutoff frequencyallowing use at a lower operating frequency or, in the presentsituation, allowing the use of a smaller aperture size. To furtherreduce the overall size of the aperture, dielectric loading is employed.The dielectric that is utilized is preferably aluminum oxide having arelative dielectric constant, e_(r), of 9.8. With the utilization ofboth a ridged waveguide and dielectric loading the aperture size issubstantially reduced with respect to the tumor thus providing greaterresolution and improved focusing.

FIGS. 4 and 5 show the dual mode antenna construction which comprises anL-band applicator 10 and a C-band aperture 12. The applicator 10, asnoted in the drawing, is in the form of a single ridge waveguide. Thiswaveguide receives a signal from the probe 14 which couples in turn tothe coax line 16. Similarly, there is provided a probe 18 associatedwith the C-band aperture 12 coupling to an associated coax line 20.

The ridged waveguide dimenions as identified in FIG. 4, are as follows:

A₁ =9.296 cm

A₂ =4.648 cm

b₁ =4.648 cm

b₂ =2.154 cm

reduced due to dielectric loading, e_(r) =9.8, to

A₁ =3.66 cm

A₂ =1.83 cm

b₁ =1.83

b₂ =0.85

The following calculated parameters apply, namely

    ______________________________________                                        λg                                                                              guide wavelength =  26.63  cm                                        λo                                                                              free space wavelength =                                                                           18.64  cm                                        λc                                                                              cutoff wavelength = 27.89  cm                                        Zo∞                                                                              characteristic impedance =                                                                        150    ohms                                               at an infinite frequency                                             Zo       characteristic impedance =                                                                        214    ohms                                      ______________________________________                                    

For a calculation of these parameters see Samuel Hopfer, "The Design ofRidged Waveguides." IRE Trans., Vol. MTT-3, No. 5; October 1955 and S.B. Cohn, "Properties of Ridged Waveguide." Proc. IRE, Vol. 35, pp.783-788; August 1947.

The insertion loss may be obtained by measuring the total loss of twoidentical transitions in series (i.e., mated at the waveguide opening).Assuming the two transitions to be equal in loss, the single transitionloss is 0.2 dB maximum. The VSWR, when held against the human body wasapproximately 1.5:1. Since the human body does not represent a fixedtermination but rather a variable match, a reflectometer is included atthe transmitter output to enable determination of the reflected andincident power levels. Both of these measured levels may be easilycombined to provide a single output reading.

The dimensions of the ridged portion of the L-band ridged waveguide areselected to allow propagation of the higher frequency associated withthe C-band radiometer. As indicated in FIG. 4, the C-band transition oraperture has dimensions of a height of 0.92 centimeters and a width of1.83 centimeters.

The plated surfaces of the dielectric-loaded C-band waveguide form andcoincide with the single ridge of the L-band waveguide as depicted inFIG. 4. The plating may be of nickel, copper or gold, for example. Withregard to the C-band aperture, the insertion loss is measured to be lessthan 0.3 dB. The VSWR, when held against the human body is less than2:1.

By placing the radiometer input witin the single ridged waveguide L-bandtransition, the point of maximum field of the source of heat is in closeproximity with the point of thermal detection. The cutoffcharacteristics of the C-band waveguide are used along with otherfiltering to form a highpass filter for isolating the highpower L-bandsource from the sensitive radiometer.

As indicated in FIGS. 4 and 5, and in particular in FIG. 5, there isprovided a heater 24 which is disposed between the applicator and theaperture. This heater may be of conventional design and is in the formof a thin sheet having associated therewith a proportional thermostatfor maintaining a constant temperature at or very near to that of thetemperature of the human body. The microwave assembly is then containedin an insulated housing 28 having indexing lines 30 on the outer surfaceas shown in FIG. 3. The indexing lines are located 90° apart on theperimeter of the housing to allow accurate positioning of the C-bandradiometer input. To allow accurate and repeatable positioning of theantenna, an indexed silk screen and frame (not shown) may be provided.The use of the tightly drawn silk screen allows flattening of theportion of the body to be scanned. The mismatch and loss associated withthis thin silk screen is negligible.

The microwave system of this invention is also quite safe to use. One ofthe characteristics of the system is that there is a large mismatch onthe order of 12:1 associated with the low impedance ridged waveguidewhen left open circuited. (i.e., in the atmosphere removed from thehuman body with its high dielectric constant to which the waveguide ismatched). Utilizing a Narda Model No. 8607 power meter placed within oneinch from the waveguide opening with the L-band power source fully on,the measured level was less than 0.4 mW/cm². The safety standardestablished by the government is 10 mW/cm² for electromagneticradiation, regardless of frequency. For example, microwave ovens arepermitted to radiate at a level of 5 mW/cm² at a distance of 2" from theoven.

Referring now to FIG. 1, there is shown a schematic diagram of themicrowave radiometer showing the signal coupled from the receiverantenna (C-band aperture) to the switch SW1. The microwave radiometerthat is depicted is of special design in accordance with the presentinvention but is generally of the common load comparison, or Dicke,type. The radiometer design substantially reduces the effects of shortterm gain fluctuations in the radiometer. The receiver input is switchedby means of switch SW1 at a constant rate between the antenna and aconstant temperature reference load. The switched, or modulated RFsignal is therefore inserted at a point prior to RF amplification and asclose to the antenna as possible; in turn, it is then amplified andcoherently detected. The final output is proportional to the temperaturedifference between the antenna and the reference load.

In FIG. 1 a second switch SW2, referred to as a calibration switch, isalso employed. With this switch, the reference load as defined by thenoise diode 36 and the fixed attenuator 38, is compared with a base load40 rather than the signal from the antenna. If the base load is equal intemperature with the reference load, the DC output of the radiometer isthus nulled to zero.

In the case where long integration times are involved, long term gainvariations in the receiver are considered. The long term; or slow, gainvariations can degrade the minimum detectable temperature sensitivity,ΔT, in accordance with the following expression: ##EQU1##

If the temperatures T₁ and T₂ are maintained approximately the same, theeffect of long term receiver gain variations becomes negligible.Therefore, it is advantageous to maintain the temperatures of both thebase load 40 and the reference load 42 approximately equal to thetemperature of the antenna.

The radiometer described herein employs at least one low noise RFamplifier in conjunction with a simple single-ended square law detectorrather than the more complex superheterodyne which employs a localoscillator and IF amplifier. The square law detector of this arrangementminimizes the potential drift and noise associated with thesuperheterodyne approach. The components that comprise the radiometerare discussed in detail hereinafter.

Associated with FIG. 1 is table I set out herein which lists theindividual components shown in FIG. 1 along with their identifying partnumber and brief description of their purpose or function.

                                      TABLE I                                     __________________________________________________________________________    ITEM             PART NO.                                                                              PURPOSE OR FUNCTION                                  __________________________________________________________________________    RECEIVER ANTENNA MA 56825                                                                              COAX TO WAVEGUIDE TRANSITION-                                                 INTEGRATED WITH TRANSMITTER                                                   ANTENNA                                              SWITCH 1         MA 56829                                                                              SPDT COAXIAL MECHANICAL SWITCH                                                GREATER THAN 60 dB ISOLATION                                                  LESS THAN 0.1 dB LOSS                                ISOLATOR 1       MA 56831                                                                              STRIPLINE FERRITE ISOLATOR WITH                                               INTEGRATED STRIPLINE TO                                                       WAVEGUIDE TRANSITION                                 ISOLATOR 2       MA 56834                                                                              WAVEGUIDE FERRITE ISOLATOR                                                    WITH INTEGRATED TRANSITION                                                    TO COAX                                              SWITCH 3         MA 56832                                                                              WAVEGUIDE FERRITE LATCHING                                                    SWITCH DICKE SWITCH                                  REFERENCE LOAD 42                                                                              MA 56836                                                                              REFERENCE LOAD COAXIAL                                                        TERMINATION WITH INTEGRATED                                                   HEATER AND PROPORTIONAL CONTROL                      BASE LOAD 40     MA 56836                                                                              BASE LOAD COAXIAL TERMINATION                                                 WITH INTEGRATED HEATER AND                                                    PROPORTIONAL CONTROL                                 FIRST RF AMPLIFIER                                                                             AMPLICA RF AMPLIFIER (FET) HAVING 2.2 dB                                      MODEL   NOISE FIGURE AND 35 dB GAIN                                           3131CS1                                                      ISOLATOR 3       MA 56837                                                                              COAXIAL FERRITE ISOLATOR                                                      20 dB MINIMUM ISOLATOR WITH                                                   LESS THAN 0.3 dB LOSS                                FILTER 44        MA 56838                                                                              STRIPLINE BANDPASS FILTER                                                     500 MHz BANDWIDTH                                    SECOND RF AMPLIFIER                                                                            AMPLICA RF AMPLIFIER (FET) HAVING 2.6 dB                                      MODEL   NOISE FIGURE AND 33 dB GAIN                                           3441CS                                                       SQUARE LAW DETECTOR                                                                            MA 56841                                                                              FIRST RF DETECTION HAVING                            AND VIDEO AMPLIFIER      20 dB VIDEO GAIN                                     LOCK IN AMPLIFIER 50                                                                           PRINCETON                                                                             PROVIDES IMPROVED SIGNAL TO                                           APPLIED NOISE RATIO THROUGH FREQUENCY                                         RESEARCH                                                                              LOCK AND NARROW BANDWIDTH-                                            MODEL   PROVIDES SYNCHRONOUS                                                  5101    DETECTION                                            SWITCH 2         MA 56829                                                                              SPDT COAXIAL MECHANICAL SWITCH                                                PROVIDING GREATER THAN 60 dB                                                  ISOLATION AND LESS THAN                                                       0.1 dB LOSS                                          NOISE DIODE 36   MSC     NOISE SOURCE - 30 dB                                                  MODEL   EXCESS NOISE                                                          MC5048                                                       FERRITE SWITCH DRIVER/56                                                                       MA 56839                                                                              PROVIDES 100 Hz SQUARE WAVE                                                   REFERENCE TO LOCK IN AMPLIFIER                                                ALSO PROVIDES LATCHING FERRITE                                                SWITCH DRIVE                                         __________________________________________________________________________

The minimum detectable temperature sensitivity, ΔT is expressed asfollows: ##EQU2##

In the case of the Dicke switch employing square wave modulation, thevalue of k is 2.0.

F=noise figure (first amplifier stage), which in our case is 2.2 dB(1.66 ratio).

L=input losses, expressed as a power ratio. The total loss is 2.0 dB(1.58 ratio).

The effective noise figure, FL, is therefore 2.2+2, or 4.2, whichrepresents a power ratio of 2.63.

T₁, is the ambient radiometer temperature (microwave portion); namely,290° K.

T₂, the source temperature (i.e., temperature seen by antenna), namely310° K.

B, the receiver bandwidth (i.e., the 3 dB bandwidth of the bandpassfilter following the first RF amplifier); namely, 500 MHz.

τ, the radiometer output time constant in seconds. Utilizing athree-second time constant, there is a minimum detectable temperaturesensitivity of: ##EQU3##

Increasing the time constant, T, to 10 seconds results in a ΔT of 0.02°K. Similarly, reducing the time constant to one second results in a ΔTof 0.07° K.

The signal level at the input to the square law detector 46 of FIG. 1 isdetermined as follows:

Noise Temp., NT=(FL-1) T_(o), °K.

F=noise figure (first amplifier stage), which in our case is 2.2 dB(1.66 ratio).

L=input losses, expressed as a power ratio.

T_(o) =ambient temperature of the radiometer, °K.

The losses at 4.7 GHz, prior to the amplifier, are as follows:

    ______________________________________                                        Antenna or Applicator                                                                              0.3   dB                                                 Cable                0.7                                                      Calibration Switch SW1                                                                             0.1                                                      Isolator/Waveguide Adapter                                                                         0.3                                                      Dicke Switch SW3     0.3                                                      Ferrite Isolator     0.2                                                      Waveguide-to-Coax Adapter                                                                          0.1                                                                           2.0   dB (1.58 ratio)                                    ______________________________________                                    

The effective noise figure, FL, is therefore 2.2+2, or 4.2 dB, whichrepresents a power ratio of 2.63.

    ∴NT=(2.63-1)290=473° K.

To calculate the noise power at the input to the radiometer, we have

P_(N) =kTB watts

k, =Boltzmann's constant=1.38×10.sup.≦ μjoules/°K.

T=473° K. (calculated above)

B =bandwidth of radiometer, Hz; namely, 500 MHz (equivalent to the 3 dBbandwidth of the bandpass filter)

P_(N) =1.53×10⁻²³ ×473×500×10⁶ 3.26×10⁻¹² watts

Converting dB, we have ##EQU4## The combined amplifier gain less theloss of the bandpass filter is 64 dB, resulting in an input level to thesquare wave detector of (-84.9+64) or -20.9 dbm which is well within thesquare law region.

With regard to the microwave radiometer schematic of FIG. 1, at itsinput there is shown the connection which is preferably by way of a coaxcable from the receiver antenna (applicator aperture) to one input ofswitch SW1. This may be termed a calibration switch which is asolenoid-operated, mechanical single pole/double-throw switch used todisconnect the antenna and in its place connect the base load 40 by wayof a second switch SW2. The switch SW1 has an isolation, or switchingratio, of grater than 60 dB with a corresponding insertion loss of lessthan 0.1 dB. The switch SW2 is used in the calibration circuit todisconnect the base load and to insert in its place the calibrated noisesource as represented by the fixed attenuator 38 and the noise diode 36referred to hereinafter.

As indicated in FIG. 1, there are three ferrite isolators used in thereceiver path. These are identified as isolators ISOL-1, ISOL-2 andISOL-3. The first isolator, is located between the calibration switchSW1 and the Dicke switch SW3. This isolator is used to terminate theoutput of the reference load when the Dicke switch is in the low lossstate. In this state, the reference or base load is circulated in thedirection of the antenna which, in this case, functions as a ferriteisolator. The isolator ISOL-1 employs a coaxial-to-waveguide transition.The insertion loss of this isolator and the transition is less than 0.2dB, with a corresponding isolation of greater than 23 dB.

The second isolator ISOL-2 in FIG. 1, is disposed between the switch SW3and the first stage RF amplifier to maintain a constant load match tothis amplifier. Any reflections from the RF amplifier would therefore beterminated in the isolator. Again, this isolator, which is a waveguideisolator with a coax-to-waveguide transition, has an insertion loss ofless than 0.2 dB with an isolation of greater than 23 dB.

There is also provided in FIG. 1 a third isolator ISOL-3 which islocated between the output of the first RF amplifier and the bandpassfilter 44. The purpose of this particular isolator is to present aconstant load match to the output stage of the first RF amplifier, andalso to present a matched input to the bandpass filter 44.

A switchable ferrite circulator, designated switch SW3 in FIG. 1, formsthe load comparison, or Dicke switch, function. A ferrite device ispreferred over a semi-conductor approach primarily in view of the lowerinsertion loss, typically less than 0.3 dB, and elimination of noisegenerated by the semi-conductor junction over and above the measuredinsertion loss.

Briefly, the device SW3 is a switchable ferrite junction circulatorutilizing the remnant, or latching, characteristics of the ferritematerial. The principle of latching action is as follows: Using theintrinsic properties of a hysterisis loop of a ferrite toroid, atransverse magnetic field is used across a portion of the ferriteexposed to an RF signal. The biasing field is actually the residualinductance of the ferrite toroid; therefore, the device needs no holdingpower and can be reversed in polarity using merely enough energy toovercome the natural coercive force of the toroid.

For the system of this invention, the latching circulator has beenconstructed in waveguide having a single ferrite element containedwithin the microwave circuit. The insertion loss is less than 0.3 dB,having isolation in excess of 20 dB.

The first-stage RF amplifier may be a four stage FET device constructedin microstrip with integrated biasing circuitry. The noise figure of thefirst amplifier (Amplica Model No. 3131CSI) is 2.2 dB with a gain of 35dB. The second RF amplifier (Amplica Model No. 3441CS) has a noisefigure of 2.6 dB, with an associated gain of 33 dB. In both instances,the noise figure includes the input ferrite isolator as depicted inFIG. 1. With the input and output VSWR at less than 1.5:1, the gaincompression at signal levels of between -55 dbm to -10 dbm is less than0.1 dB.

In FIG. 1 the filter 44 is a bandpass filter and the bandwidth of themicrowave radiometer is basically determined by the bandpasscharacteristics of this filter. The filter is disposed after the firststage of RF amplification to minimize the impact of the insertion lossof the filter on the overall system performance. The filtercharacteristics are chosen to minimize possible interference due tonearby microwave communications or radar bands. FIG. 6 shows the filtercharacteristics. The filter is preferably an 8-section bandpass filterconstructed in stripline. The pass band loss is less than 3 dB and thebandwidth is approximately 500 MHz.

As indicated in FIG. 1, there are basically two loads provided, a baseload 40 an a reference load 42. The load design is coaxial, employing astainless steel RF connector to provide thermal isolation betwen theload and the remainder of the system. The coaxial termination iscontained within an insulated housing and utilizes an integrated heaterand proportional control to maintain constant temperature. The absolutetemperature of both the base and the reference loads is monitored anddisplayed on a digital temperature indicator (not shown).

The calibration circuit comprises a precision, solid state, noise sourcehaving an excess noise ratio, ENR of 33 dB. This allows noise to beinjected into the receiver front end via the high isolation mechanicalcalibration switch. The output level of the noise source is reducedthrough the use of a precision calibrated pad (43.3 dB). Thiscalibration circuit is shown in FIG. 1 as including a fixed attenuator38 and the noise diode 36.

The temperature sensitivity of the noise diode is less than 0.01 dB/°C.

The apparent output noise temperature, T_(NO), at the SPDT switch is##EQU5## where

T₁ =temperature, ambient, of the source; namely, 273.13+22.25° or295.38° K.

T₂ =temperature of component in lossy path; namely, 295.38° C.

ε=emissivity or, in this case, excess noise ratio (ENR) of the noisesource (33 dB corresponds to a ratio of 1995)

L=attenuation expressed as a power ratio (43.3 dB corresponds to a ratioof 21,380); therefore, ##EQU6## thus providing a 12.76° differentialwith respect to the base load of 310° K.

The lock-in amplifier 50 shown in FIG. 1 is one made by PrincetonApplied Research, Model No. 5101. This amplifier enables the accuratemeasurement of signals contaminated by broadband noise, power linepickup, frequency drift or other sources of interference. Itaccomplishes this by means of an extremely narrow band detector whichhas the center of its pass band locked to the frequency of the signal tobe measured. Because of the frequency lock and narrow bandwidth, largeimprovements in signal-to-noise ratio are achieved. This allows thesignal of interest to be accurately measured, even in situations whereit is completely masked by noise. In addition, the lock-in amplifier 50provides the synchronous function associated with the Dicke switch;i.e., the unit supplies the 100 Hz reference clock frequency to drivethe ferrite switch driver.

The system is provided, of course, with a power supply comprising three12-volt, 50 amp. maintenance free, lead-acid batteries in series, fusedat 10 amps per battery. The outputs from the battery assembly include12, 24 and 36 volts. These voltages are appropriately applied to thereceiver, lock-in amplifier and transmitter. There may also be provideda voltage converter and regulator. Status indicators may be employed forindicating operating voltages. The main operating switch may have threepositions including an on position, an off position and a "charged"position. In the charged mole, a meter is used to monitor the chargecurrent to the batteries which is limited to approximately 6 amps. Witha 3-9 amp-hour discharge rate (a normal 8 hour operate mode), therecharge cycle is approximately 10-12 hours (overnight).

The microwave transmitter embodied in the system of this invention isshown in FIG. 2. This is an L-band transmitter operating at a frequencyof 1.6 GHz. The transmitter includes a 1.6 GHz, 30W, solid state source60 which couples to an RF power amplifier, filter, and microwavereflectometer. There are two series connected filters 66 and 68 whichare low-pass filters connected in series for providing 120 dB ofattenuation at the third harmonic. The third harmonic of the 1.6 GHzsource is 4.8 GHz, which is within the radiometer passband. It isintended that the microwave transmitter operates simultaneously with themicrowave radiometer to provide localized heating of subsurface tissue,while simultaneously monitoring the temperature with the radiometerdescribed previously. The reflectometer employed in the transmitter ofFIG. 2 allows determination of both the reflected and incident powerlevels. The detector 70 measures the incident leve while the detector 72measures the reflected level. FIG. 2 also shows the output terminal 74which is the RF output coupling to the applicator.

The output power level from the transmitter of FIG. 2 is adjustable from0 to 25 watts (measured at the input to the L-band antenna) and,therefore, includes all microwave circuit and coaxial cable losses. FIG.7 illustrates the approximate power input plotted as a function of"output level" control setting. This measurement is made into a matchedload and, therefore, to be more accurate is reduced according to theload mismatch. A 2.1 load VSWR, for example, corresponds to a 10% powerreflection. For an "output level" setting of 70 which corresponds to 10watts (per FIG. 7), therefore, there are actually 9 watts of incidentpower with 10% or 1 watt reflected. The reflected energy is terminatedin the load associated with the second ferrite isolator 64.

The VSWR (voltage standing wave ratio) is obtained from the followingexpression: ##EQU7## where P_(R) and P_(F) are obtained from the heaterefficiency meters "Reflected" and "Forward" respectively.

The ratio of the reflected power, P_(r), to the incident power, P_(i),is determined as follows: ##EQU8## where the total power generated isequal to P_(r) +P_(i).

The filter/reflectometer 71 shown in FIG. 2 is a microwave integratedcircuit such as one by Microwave Associates Model No. MA-56823. This andother parts are identified in the enclosed Table II which shows theprimary elements of the transmitter of FIG. 2, their part number and abrief description of their function or purpose.

                                      TABLE II                                    __________________________________________________________________________    ITEM          PART NO.                                                        __________________________________________________________________________    1.6 GHz SOURCE                                                                              MA-56826                                                                            THE ENTIRE ASSEMBLY FORMS THE                                                 1.6 GHz SOLID STATE 30W SOURCE.                           RF POWER AMPLIFIER                                                                          MA-56829                                                                            THE OUTPUT LEVEL IS ELECTRONICALLY                                            VARIABLE.                                                 ISOLATOR - FIRST                                                                            MA-56827                                                                            COAXIAL FERRITE ISOLATOR -                                                    PROVIDES INTERSTAGE ISOLATION                                                 BETWEEN FIRST AND SECOND RF                                                   AMPLIFIERS 0.2 dB LOSS, 20 dB                                                 MINIMUM ISOLATION                                         ISOLATOR - SECOND                                                                           MA-56822                                                                            COAXIAL FERRITE ISOLATOR - PROVIDES                                           ISOLATION BETWEEN THE SOLID STATE                                             SOURCE AND THE EXTERNAL LOAD                              FILTER        MA-56824                                                                            LOW PASS FILTER - PROVIDES THIRD                                              HARMONIC REJECTION OF GREATER                                                 THAN 60 dB.                                               FILTER/       MA-56823                                                                            LOW PASS FILTER - PROVIDES ADDITIONAL                     REFLECTOMETER       60 dB THIRD HARMONIC REJECTION.                           ASSEMBLY            COMBUSTION OF DIRECTIONAL COUPLERS                                            AND DETECTOR ALLOWS MEASUREMENT                                               OF FORWARD AND REVERSE POWER.                             __________________________________________________________________________

The filter/reflectometer assembly 71 is depicted as having four portsincluding an input port 1 and an output port 2. At a frequency of 1.6GHz, the insertion loss from Port 1 to 2 is 0.33 dB, the VSWR of Port 1and 2 is less than 1.15. The coupling between Ports 1 and 4 and Ports 2and 3 is approximately 40 dB. The coupler associated with Port 4 is,therefore, used to measure the reflected power, whereas the couplerassociated with Port 3 is used to measure the incident power. Thedirectivity of the two couplers is 28 and 16 dB respectively. Matchedcoaxial detectors (HP Model 8472B) are mated to Ports 3 and 4, theoutput of which is applied to the current meters for registeringreflected and incident power levels. These meters are not shown in theschematic of FIG. 2.

As previously mentioned the low pass filters 66 and 68 provide thirdharmonic rejection. The attenuation due to the low pass filtering isgreater than 60 dB at 4.8 GHz.

As mentioned previously, there is a heater 24 depicted in FIG. 5 as usedfor maintaining the dual mode antenna 10 at a constant temperature closeto the human body temperature. When the system is in its charged mode ofoperation the heater 24 is maintained operating as are heatersassociated with the reference load and the base load. This eliminatesany need for an extensive "warm-up."

The lock-in amplifier 50 may have associated therewith certain controlsand a meter. One of the controls is a signal sensitivity control. Thenext control is an offset control which allows zeroing of the meter.Another control that may be provided is a time constant pre-filtercontrol which can be normally set in the one or three second position. Afurther control is a reference control. The last control is a modeselector control.

With regard to the transmitter of FIG. 2, there are controls associatedtherewith. These controls include an on-off switch which is used toactivate the transmitter and a ten-turn control to adjust the outputlevel. A control knob allows adjustment of one of the meters associatedwith the transmitter to full scale to monitor the applicator efficiency.The ratio between the two meters associated with the transmitterindicates the heater efficiency.

The dual mode microwave system depicted in FIGS. 4 and 5 includes twoantennae 10, 12, heater 24, and proportional thermostat not shown inthat drawing which is cabled back to the receiver and transmitter. Thetwo antennae are a transmitter antenna or heat antenna and a receiverantenna. The heater 24 is self-contained within the applicator body andis used to maintain the applicator at body temperature. There isassociated with the heater a thermostat, as mentioned, for maintainingthe proper temperature at the applicator. FIG. 5 shows schematically theconnection of the thermostat between the heater 24 and an electricalsource.

The waveguide constructions, such as shown in FIGS. 4 and 5, arepreferably of a ceramic material such as aluminum oxide with the outerboundaries of the waveguide being formed by means of a metallic platingon the ceramic. This plating may be of nickel, copper or gold. Thisarrangement is depicted in FIG. 4 by a small cut-out portion showing theplating and the ceramic material. With the L-band waveguide constructionbeing essentially fitted within the C-band waveguide construction, onlya single plating is necessary between the components.

One of the advantages of the present invention is that with this system,integrity is maintained between the applicator and the aperture withoutinterference occurring between transmitted heating signals and detectedsignals. In this way the microwave heating signal can be maintainedessentially "on" at all times without any necessity for interruption ofthis signal for detecting temperature.

The two frequencies that have been selected herein, one in C-band andone in L-band have not been selected indiscriminately but rather havebeen selected based upon such factors an emissivity, spatial resolutionand transmission characteristics. For example, the microwave heatingfrequency has preferably been selected lower than the radiometerfrequency as the lower heating frequency provides a deeper penetrationof microwave heating. On the other hand, the radiometer frequency isselected higher preferably because at the higher frequency there is anincreased resolution which is desired for detecting, in particular, asmall temperature differential.

A further embodiment to the present invention is described in FIGS. 8, 9and 10. This embodiment describes a microwave endoscope for the internaldetection and treatment of cancer. This apparatus, is used inconjunction with the basic microwave system described hereinbefore topermit detection and/or treatment of internal cancer tissue. One of theadvantages of the this technique which involves use in conjunction withthe endoscope, is the avoidance of high microwave absorptioncharacteristics associated with muscle and other tissue exhibiting highwater content when an application is external.

In the disclosed embodiment, reference is made to the adaptation of thedetection system in association with a bronchoscope. However, it shouldbe understood that the technique may also be supplied with otherspecula, such as a protoscope.

FIG. 8 is a cross-sectional view through a bronchoscope 80 showingfiberoptic light guides 82 and 83 along with an objective lens 84. Thereis also provided a biopsy forceps channel 86 which is adapted toaccommodate the system of this invention. The bronchoscope withfiberoptics enables an endoscopist to use the biopsy forceps forhistodiagnosis. As shown in FIG. 8, the distal end of the bronchoscopehas either one or two fiberoptic light guides which, when connected to asuitable light source, serve to illuminate or transmit light. At thesame time the objective lens is used for viewing. Normally the biopsyforceps channel serves as a guide for the biopsy forceps. The mechanicalpositioning of the distal end of the bronchoscope is conventional and iscontrolled externally from a known control unit. The control unit andthe distal end are connected by a long flexible cable (not shown).

In accordance with the endoscopic embodiment of the invention there isprovided a microwave transmission line the end of which is shown in FIG.9 essentially in the form of a coax cable having an inner conductor 87,an outer conductor 88 and an intermediate dielectric 89. Thistransmission line couples to a radiating or coupling element twodifferent versions of which are shown in respective FIGS. 9 and 10. Thistransmission line with associated radiating element is interchangeablewith the biopsy forceps for insertion into the biopsy forceps channel 86of the bronchoscope, proctoscope or other type of similar device adaptedfor endoscopic work. The radiating element, discussed in detailhereinafter, is designed to provide efficient coupling of microwaveenergy to or from the human tissue. When used with a microwaveradiometer as described herein before, there is provided accuratemeasurement of the temperature of the tissue in the vicinity of theradiating element. Thus, the endoscopic version is also adapted for usein a dual mode wherein the radiating element is used for the applicationof heat and thereafter may be used for the detection of temperature. Thedevelopment of this dual mode system provides a passive detectiontechnique for use in early detection of cancer. In addition, the systemhas the capability of providing localized heating of subsurface tissuetaking advantage of the differential heating associated with the thermalcharacteristics of tumors as discussed herein before.

Depending upon the location of the cancerous tissue, it has been foundthat for many applications it is more desireable to provide detectionand/or treatment endoscopically. The human body consists of basicallythree layers including a thin layer of skin over a thicker layer ofsubcutaneous fat, in turn over a layer of muscle or other tissue of highwater content. The pore microwave transmission characteristicsassociated with the muscle (i.e., high loss tangent and high dielectricconstant) make it desirable to monitor temperature or apply localizedheating from within the human body, thereby avoiding propogation throughthe high loss muscle tissue. Thus, there is described in this finalembodiment of the invention a system for internal use that combines asuitable microwave coupling in conjunction with an existing bronchoscopeor the like. Coupling in close proximity to the tumor eliminates theproblems associated with high transmission losses in the tissue media,allowing greater freedom and selection of frequency. It also allows theuse of much lower power levels to achieve the elevated temperature. Inthis way it is possible to elevate the temperature of the tumor toapproximately 50° C. while avoiding increased temperatures is nearbytissues or organs.

With reference to FIG. 9 there is shown one embodiment of the radiatingelement. Previously it has been mentioned that there is a coaxial lineincluding inner and outer conductors and a central dielectric. The innerconductor terminates in a forward end launch 90. The outer conductorsconnect to a conductive ring 92 which carries a ceramic end 94. The endlaunch 90 is fitted within the ceramic portion of the radiating element.The outer ceramic of the element is preferably polished to preventinjury to the bronchiole wall when the radiating element protrudes fromthe distal end of the bronchoscope. The center conducter protrudesbeyond the end of the outer conductor of the coaxial transmission lineto serve as the launch or radiating element both in the embodiment ofFIG. 9 and that of FIG. 10. The ceramic tip serves as both a mechanicalsupport and guide as well as a matching device. The dielectric constantassociated with the ceramic results in a reduced tip size and becomes anintegral part of the matching strucure to the human tissue, therebyaccomplishing efficient microwave coupling.

The alternate embodiment of the radiating element, which is of loop typeis shown in FIG. 10. Again, this element includes inner and outerconductors. The inner conductor 87 extends in a loop 91 and forms thebasic radiating element of the structure. This loop is supported by atleast the ceramic portion 93 of the radiating element. The other end 95of the loop is secured to the conductive ring 92. The loop embodiment ofthe radiating elements operates substantially the same as the previouslydescribed end launch embodiment.

The apparatus of the present invention may be in particular used for thedetection of breast tumors. Such tumors having a diameter of less thanone cm or approximately 0.5 cm have been detected. Such tumors have notbeen capable of detection with normal zero-mammographic techniques. Inone patient having two primary breast tumors, the smallest tumormeasured 2.5° C. higher than the surrounding tissue whereas the largertumor, which was also identified by zero-mannography, measured 1.2° C.higher than the surrounding tissue. This adds credibility to theprobability that small tumors are metabolically more active andrepresent a more concentrated hot spot.

In review of the technique of this invention, it has been mentioned thatenhancement of the tumor is provided by the application of heat via theapplicator. When this heat is applied there may initially be atemperature differential between the tumor and the surrounding tissuethat is relatively small; that is the differential temperature isreduced. However, in accordance with the method of this invention it ispreferred that a waiting period occur which may be approximately fiveminutes following the application of heat to measure the temperaturedifferential. For example, on data taken on a large rabbit, the initialtemperature differential was 1.2° C. whereas after the five minutewaiting period the temperature differential was then 1.8° C. Due to theimproved vascularity of the normal tissue with respect to the tumor, thenormal tissue has been found to return to its normal temperature, whilethe tumor itself remains at an elevated temperature. This demonstratesthe ability to enhance detection through application of heat accompaniedby a waiting period such as one on the order of five minutes for theactual sensing of temperature.

What is claimed is:
 1. A microwave transducer for applying energy to andreceiving energy from living tissue, said transducer comprising:amicrowave transmitter, a radiating element, a microwave radiometermeans, a section of transmission line coupled to said radiating element,said radiating element comprising a dielectric impedance-matching meansfor substantially matching said radiating element to said tissue butsubstantially mis-matching said radiating element to air, saiddielectric impedance matching means having a smooth end tip, meanscoupling the microwave transmitter to the end of the transmission lineremote from said radiating element and for establishing at the radiatingelement a heating temperature over a predetermined heating period andgreater than the normal human body temperature, means coupling themicrowave radiometer means in common with the microwave transmitter tothe remote end of the transmission line, said microwave radiometer meanscomprising means for sensing temperature at a resolution of fractions ofa centigrade degree, in combination with an endoscopic guide meansadapted for passage into an opening in a living body, said guide meansincluding a passage for said transducer and said transmission line, andcarrying observation means and light transmission means whereby saidtransducer may be placed in an observable-operative position within thebody, said means for sensing temperature being operative to register atemperature differential only after a predetermined waiting periodfollowing said predetermined heating period so as to increase thetemperature differential measurement, said section of transmission lineincluding an inner conductor and an outer conductor, said radiatingelement having a launch means coupled from the transmission line innerconductor and extending beyond said transmission line outer conductor,said radiating element dielectric impedance-matching means having asmooth tip for holding said launch means.
 2. A microwave transducer asset forth in claim 1 wherein said light transmission means comprisesfirst and second light guides and said observation means comprises anobjective lens with the lens guide means passage being diametricallydisposed as well as the first and second light guides.
 3. A microwavetransducer as set forth in claim 1 wherein said radiating element isused and operable for both cancer detection and cancer treatment.
 4. Amicrowave transducer as set forth in claim 1 wherein said microwavetransmitter and microwave radiometer operate at different frequencies.5. A microwave transducer as set forth in claim 4 wherein the outputheating frequency associated with the microwave transmitter is less thanthe detection passband frequency associated with the microwaveradiometer.